Plants annual or biennial; tufted, not mat-forming. Culms 5–50 cm, erect to decumbent. Ligules 1–2 mm, obtuse to truncate, entire; blades 2–6 cm wide, flat or folded. Panicles 2–10 cm, contracted at matur-ity, lower branches ascending, spikelet-bearing nearly to the base; pedicels scabrous, sometimes only slightly so, sometimes with tumid epidermal cells. Spikelets 4–9 mm, with 2–6 florets. Glumes rounded to keeled over the back, midveins obscure or prominent, extending to the apices, often scabrous distally, lateral veins obscure, apices acute to obtuse; lower glumes 1–2 mm; upper glumes 2–3.2 mm; calluses with a few hairs; lemmas 2.5–4 mm, somewhat coriaceous for most of their length, glabrous or sparsely hairy on the lower 1/2, particularly along the veins, backs rounded to keeled, 5-veined, midveins and sometimes all veins prominent, midveins extending to the margin, often excurrent, apical margins hyaline, smooth to densely scabrous, apices acute to obtuse, entire; palea veins shortly ciliate proximally, shortly ciliate to scabrous distally; anthers 0.8–1.2 mm. 2n = 42.
Puccinellia rupestris grows in coastal and noncoastal habitats in Eurasia; North American collections were apparently introduced in ballast.